White roofs, aka cool roofs, are a “hot” topic these days as a means to help stem global warming. Most of us know better than to wear black on a hot day, but when it comes to the roofs on our houses, temperature often takes a back seat to aesthetics . Dark roofs mean higher air conditioning bills, and higher carbon dioxide emissions as a result. The good news is you can save money and help protect the planet by lightening the color (and therefore the temperature) of your roof, or by switching to a white roof the next time your house needs a new hat.

The Benefits of a White Roof

Switching to a white roof can actually reduce energy use by about 20 percent in hot, sunny weather, according to the Lawrence Berkeley National Laboratory Heat Island Group in Berkeley, Calif. Hashem Akbari, the Heat Island Group’s lead scientist and a professor of Building, Civil and Environmental Engineering at Concordia University in Montreal, says that transitioning to reflective roofing and pavements in the world’s urban areas would offset the equivalent of emissions from the planet’s 600 million cars for the next 18 years. A 1,000-square-foot cool roof saves air conditioning use that otherwise would emit about half a ton of carbon dioxide per year. (The average total square footage of a home in the United States is more than 2,000.)

In urban areas, white roofs also help lower smog levels by lowering local temperatures, which tend to be higher due to the large proportion of paved surfaces.

Critics have suggested white roofs do more harm than good in colder climates. But research shows that the heating benefits of a dark roof in the winter are negligible because days are shorter, skies are cloudier, the angle of the sun is low, and sometimes roofs are covered in snow. “The amount of heat savings you may lose in the winter would be, at the maximum, 30 percent of the summertime savings,” Akbari says. “If you need cooling in the summer and heating in the winter, no matter where you are, a white roof will most likely save you money.”

Cool New Roof Options

“Cool” is the buzzword that encompasses a range of roofing materials that can reduce carbon footprints. And cool roofs come in a variety of light colors.

The best time to install a cool roof is when a new roof is needed or major roof maintenance is in order. According to researchers, there’s little difference between the cost of roof colors.

Not ready for a new roof but still want to cool down? Install a white roof coating instead. There are a number of coatings that will substantially improve an existing roof’s reflectance/emittance. Plus, coatings protect and seal, potentially extending the life of your roof. The installed cost of coating a roof is about $0.50 to $1 per square foot, according to Akbari, which will be paid back by lower energy bills and the extended life of your roof.

Roof Resources

A cool roof is measured by two properties: reflectance (the ability of the product to reflect energy away from the roof) and thermal emittance (the roof’s ability to radiate absorbed heat). Ideally, you want your roof to be high in both.

Federal and state rebates are available; check the Database of State Incentives for Renewables & Efficiency for details specific to your project. Also call your utility company to check for local programs. “This will not be the silver bullet that solves the global warming problem,” Akbari says. “But it cools your home, cools your community and helps cool the globe while putting money in your pocket.”

White roofs reflect a tremendous amount of the sun's rays. However, insulating underlayment does the bulk of the work as far as keeping temperatures down is concerned. There is an effect known as a "heat island" which is the cumulative effect of radiant heat and energy keeping surrounding temperatures hotter longer in the day. This is seen commonly in cities like College Station due to the expansive swaths of concrete sidewalks and buildings. If areas and municipalities would adopt white roofs, http://www.schulteroofing.com/college-station-roofer could really help the greenhouse effect.

STEPHEN RHUDY

3/16/2012 7:21:31 PM

I've been living in NC for over 40 years. I've never understood WHY 95% of buildings have dark roof covering. In a climate where temps can be in the high 70's to mid 80's 8 months of the year, and into the low hundreds the rest of the time, a WHITE roof would seem to be a no brainer.

annie31328

4/16/2011 12:35:05 PM

For emelle_3: Get some solar shades that prevent 90% of the solar gain and are still translucent. Before you purchase any, find out what they're made of. You also don't want a lot of pvc inside the house.

hank roberts

9/22/2010 12:13:38 AM

I tried Google and did not find "Cool Roof Castastrophe" article by Tom Hutchinson referred to above -- Google only finds the one mention of it in this page.
Does anyone have a link or a summary?
Yes, I'm about to put on a white roof ..... right now I'm trying to figure out whether half inch plywood is adequate over 32" separation, to replace the old 7/8" or so planks where they're bad. Roofer plans on doing it.
Half inch? really?

R S_5

8/20/2010 6:45:33 PM

Lighter color roofs have other advantages.
A dark roof becomes a "black body radiator" at night and sheds heat faster than a light color roof. Both summer and winter. What ever heat you gain with the dark roof in the winter daylight - you lose more heat at night than the lighter color roof. (Remember - night is longer than day in the winter)
The thermal "swing" due to a dark roof absorbing and shedding heat also requires greater expansion and contraction in the roofing materials and the structuree below. Lighter color roofs last longer than an equal quality dark roof - north or south.
Most importantly, in a good building, a roof does nothing more than keep the insulated space underneath it protected from the weather - primarily rain and wind. Never use the roof surface as a thermal mechanism for the space contained below. An ideal attic space's temperature matches the outdoor temperature.
So, in an ideal building the roof color only matters to extend the life of the roof.
Build smarter - worry about the important things. Next question - what's the proper insulation thickness and material for an attic floor? You may be suprised how little
insulation is enough and how adding more may save very little energy (but can burn your cash)

George_41

5/11/2010 2:46:25 AM

I have a question: If a white roof reflects all that heat, where does the heat go? Doesn't it get reflected back into the atmosphere, which traps the heat, reflecting it back down to earth again? It seems this would create as much of a problem as it solves. At least with a dark roof and pavement, the earth can be used as a heat sink.

Bud_3

3/22/2010 5:17:07 PM

I have a 300K RSF building with a white plastic roof that was installed about 2 years ago. The roof is no longer white due in large part to the airport across the street and other debris that usually floats around in the Texas wind. I am trying to find out what a dirty roof is costing me each year vs. the nice reflective roof that we once had. I cant seem to find this information on the internet? I have a proposal to clean the roof and want to find out how long it will take to receive a payback on the cleaning vs. energy costs of having an off white roof.

Emelle_3

1/29/2010 3:57:23 PM

I live in a 4th floor apartment next to a 3-story building with the reflective “energy saving” coating, and ever since they applied the stuff, my apartment’s been about 12-15 degrees HOTTER than usual. Why? Because the reflective, silvery coating is bouncing all the magnified sunlight back up through all my windows. In the summer, we might have to resort to air conditioning the WHOLE apartment (something we’ve NEVER done before). If not, we’ll have to use room darkeners and live like vampires. I can’t believe no one anticipated this, either–save one person energy, make their neighbor use a hundred times MORE electricity. Any energy saved by my neighbor’s building will be offset by the fact that this summer, I will have to use about 10x more electricity than ever before!

Christopher_13

12/27/2009 4:45:43 PM

As a former architect and Vice President of a commercial roofing company who installed both white and black membranes, I can honestly say that white roofing does NOT make sense for the majority of the country. While a white roof may prove a real benefit if you live in southern FL, TX, AZ, or CA, the rest of the country just isn't hot enough, long enough.
The Govt's beating of the "white roofs now" drum, and the less-than-realistic "data" they show to support it is simply irresponsible. Cooling a building is cheaper than heating it, and thats why black roofs make sense for everything north of, say, Atlanta. Here's some examples to ponder:
Degree days: Where I live in the Midwest, our utility company says we have 5 times the heating degree days over cooling days. Does white or black sound better?
Walmart: They used to roof everything south of I-40 with white, north with black. Now they are all white....but what they don't mention is that all new or reroof projects are specified with 3 times the code required insulation on the roof deck. I know, because they were a client.
Google up "Cool Roof Castastrophe" article by Tom Hutchinson. It will open your eyes.
While it is true that white roofing will help some, it is NOT by far any type of panacea that the govt. is making it out to be. I'll keep my black slate, thankyou.

hazel Watson_2

11/15/2009 6:19:38 PM

For many years every time I've had choices for the roofs of my houses, whether replacing a roof or having a house built, I've always chosen the lightest color available. White was never an option.
It comes as a surprise to me that those who should know about these things are just now recommending white.

Lee_21

11/15/2009 11:08:31 AM

I was wondering what effects the white roofing or the reflective cool roofing would have on general aviation. When the pilot looks down for visual verification to a reference point would it reflect the sunlight in the eyes of a pilot.

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